How to switch my iphone 4s to straight talk?

The phone is currently not being used by any company but was originally with AT&T
i have a straight talk number and phone and was wondering and hoping someone could help me transfer my straight talk number to this iphone4s. Any help would be great.

So much as the phone has a clean ESN, you just need to get Straight Talk's BYOD SIM card kit, and follow the instructions, making sure to correct the APN settings so that you can use data.